This invention relates to a type of automotive shock absorber commonly called a McPherson Strut. The invention concerns a McPherson strut with damping characteristics that decrease upon rapid acceleration of the part of the strut connected to the vehicle wheel. It also concerns fluid flow or pressure sensitivity, in addition to acceleration sensitivity in the strut.
Hydraulic shock absorbers are essentially universally employed in automotive vehicles. Each wheel of the vehicle is coupled to the vehicle chassis or frame by a spring so that bumps or dips in the road are not transmitted directly to the passengers or vehicle load. A spring alone, however, would still give a rough ride. Shock absorbers are therefore mounted in parallel with the springs to damp the accelerations applied to the chassis from the wheel. There is a long history of shock absorber development to obtain desired characteristics of passenger comfort, handling for steering, road traction and the like.
Most shock absorbers are designed to have a certain operating characteristic or load-velocity curve which is a compromise of the characteristics desired for a variety of road conditions. The characteristics suitable for driving on relatively smooth road may, however, be inappropriate where the vehicle wheels may encounter short range bumps or dips. Such conditions are not limited to vehicles like those used on off-road terrain, but also include ordinary passenger and freight vehicles which may unexpectedly encounter chuck holes, speed bumps or foreign objects on the roadway.
In the prior applications, there are described shock absorbers which respond to accelerations of a vehicle wheel for providing automatic adjustment of orifices in the shock absorber for changing the characteristics of the shock absorber when it encounters compression or extension due to terrain defects. A single tube shock absorber with a piston in a cylinder and an acceleration sensitive mechanism in the piston is described in U.S. patent application Ser. No. 07/798,036. An acceleration sensitive twin tube shock absorber is described in U.S. patent application Ser. No. 07/878,850.
Another type of shock absorber used on a variety of automobiles is a McPherson strut. This is a type of twin tube shock absorber with the tubes connected to the wheel of a vehicle and the piston connected to the vehicle body. There are metered orifices in the piston which control the flow of fluid during compression or extension of the strut, thereby controlling the damping characteristics. A pressure relief foot valve at the lower end of the strut allows free flow of fluid from the annulus between the tubes to a chamber below the piston in the inner tube during extension of the shock absorber. During compression, the foot valve has a metered orifice that opens at a substantially higher pressure than the orifice in the piston to assure that fluid is forced through the piston during compression. A standard McPherson strut does not require gas pressurization for preventing cavitation.
The annular space between the inner and outer tubes of a McPherson strut is quite narrow, thus there insufficient space for acceleration sensitive valving as described in the prior applications. Acceleration sensitive shock absorbers have demonstrated a remarkable ability to improve the performance of vehicles equipped with such shock absorbers. It is, therefore, desirable to provide a similar arrangement or a vehicle which employs McPherson struts.